AB0964 THERAPEUTIC DRUG MONITORING OF INFLIXIMAB IN INFLAMMATORY RHEUMATIC DISEASES: REAL-LIFE DATA IN A COHORT OF PATIENTS
Authors: M. Martin Lopez, N. Molina Esteban, O. Cabrera, J. L. Pablos
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Therapeutic drug monitoring (TDM) could be helpful in several clinical situations such as loss of response to therapy, the interpretation of side effects to therapy and to determine dose adjustments <sup>[1]</sup>. <h3>Objectives</h3> To investigate the influence of demographic and clinical characteristics on circulating infliximab (IFX) levels and the clinical relevance of measuring IFX trough levels (ITL) in patients with inflammatory arthritis treated with IFX. <h3>Methods</h3> Unicentric observational retrospective study conducted in a tertiary hospital between January 2018 and December 2022. Patients with spondyloarthritis (SpA) and rheumatoid arthritis (RA) treated with IFX and having been performed a serum ITL determination during follow-up were included. Patients were classified into two groups depending on the disease activity, descriptive statistics and a comparative analysis were performed. The continuous data were compared using the Mann-Whitney U test or the Student t-test, and the frequency data with the Pearson χ2 or Fisher exact tests. Univariable and multivariable logistic regression models were employed to investigate the influence of demographic and clinical characteristics in ITL and immunogenicity. Serum dependent ROC curves were used to determine the ITL that best predicted good clinical response. <h3>Results</h3> A total of 91 patients, 78 SpA and 13 RA were included. Their demographic and clinical characteristics are shown in Table 1. All patients who had remission or low disease activity (LDA) in the ITL measurement remained without activity at 12 months. 34 of 41 (83%) patients with disease activity achieved remission or LDA at 12 months of ITL measurement with a significant improvement in the disease activity (p &lt;.001). In the univariable analysis, the presence of rheumatoid factor (OR 0.1; CI95% 0.03 – 0.7), methotrexate use (4.5; 0.8 –2.5), sulfasalazine use (7.7; 1.3 – 4.4) and disease activity (0.06; 0.02 – 0.2) are associated with ITL (p &lt;.1). Regarding immunogenicity, we observed an association with female sex (2.5; 0.8 – 7.6), rheumatoid factor (1.8; 3.7 – 8.6), ACPA positive (4.1; 0.9 – 1.9), disease duration (0.9; 0.9 – 1.0), IFX duration (0.8; 0.7 – 0.9), baseline SpA activity (2.9; 0.9 – 9.2) and disease activity (31.4; 3.9 – 2.5), all p &lt;.1. However, in the multivariable analysis only was confirmed the association between ITL and immunogenicity with disease activity, and between immunogenicity with IFX duration (p &lt;.05). In our cohort, the optimal cut-off of ITL in RA patients was 1.5 μg/mL and 6.7 μg/mL for SpA (Fig). <h3>Conclusion</h3> TDM appears to be a useful technique for the control of inflammatory arthritis. Demographic and clinical characteristics can influence drug levels that are important to know to decrease immunogenicity when possible. More studies still need to be carried out to analyze the therapeutic range of biologics. <h3>Reference</h3> [1]<i>RMD Open.</i> 2022;8(2):e002216 <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> None Declared.